The primary products of timber industry, such as various kinds of sawn timber, veneer, and wood waste, that are produced for further use, usually have a moisture content above the saturation limit of the fiber. In this state timber is not suitable for further processing or shaping, therefore the moisture content has to be reduced by natural or artificial drying to under the saturation limit of the fiber to the air-dry (12-18%) or the room-dry (6-12%) state. The rapid increase in industrial use of wood products and the need for producing components of room-dry state made it essential to accelerate the slow natural drying process that usually lasts for at least 2 to 5 years, by the use of various artificial drying methods.
The acceleration of the natural drying processes (temperature, wind, humidity) has not led in an unchanged form to a good result, therefore various methods have been developed to remove the moisture from the wood as quickly and carefully as possible. Nearly all these methods are based on modifications of the properties and parameters (temperature, speed of air current, pressure, humidity) of the surrounding air, except for high frequency drying in which drift of the moisture begins from the inside.
Known artificial drying methods include:
convection drying, PA1 condensation drying, PA1 vacuum drying, PA1 high frequency drying, and PA1 drying in hot oil. PA1 heating, PA1 drying, and PA1 compensation (and conditioning, cooling). PA1 macroscopic features and defects in the wood result in inaccuracy in the achieved value (usually in the order of 1-5%), PA1 wood undergoes different deformations during drying (e.g. bending, warping, splitting, of butt or pith, etc.) because of the accelerated reduction of moisture content, PA1 tensions of different types and scales emerge during drying and remain until processing when further bending and warping take place, and PA1 the effects of the changes in the surrounding humidity, the achieving of balance in the moisture content of the wood, and other changes in the humidity (e.g. moistening) have the result that the artificially dried material changes its shape and dimension to a larger extent than naturally dried material.
The first three procedures are generally used in practice. Each of them is suitable for reaching the required degree of humidity by changing various parameters of time and space. Quick drying of "dry" timber, which is quick compared with natural drying, usually involves three main phases:
The moisture content of timber dried by the aforementioned methods can be adjusted to the required level, but